We primarily use data reported via the World Meteorological Organization's Voluntary Observing Ship (VOS) program to provide a snapshot of current weather conditions at sea, worldwide. This data can also be used to track the progress of ships at sea. Many ships do not report their weather observations to WMO, or report only sporadically; these ships will not have records in our database. Additional information comes from the YOTREPS network of cruising yachts; YOTREPS positions are updated only once per day.
This site tracks all (friendly) ships at sea... including freight liners.
Weather observations and positions of ships at sea